The present invention relates to the use of an unsupported metallocene catalyst for the polymerization of stereoregular olefins in the gas phase.
U.S. Pat. No. 5,504,232 to Winter et al. teaches that bridged substituted bis-indenyl type metallocene complexes may be used to polymerize propylene to produce a stereoregular polymer, but given the inventors"" later work as disclosed in Spalek et al., xe2x80x9cThe Influence of Aromatic Substituents on the Polymerization Behavior of Bridged Zirconocene Catalysts, Organometallics 1994, 13, 954-963, it is not clear whether such stereoregularity is transferable outside the specific conditions of the slurry phase since solvent effects may play a large role in the polymerization. Additionally, appropriate conditions for polymerizing outside of the liquid phase are not taught.
U.S. Pat. No. 5,317,036 teaches the gas-phase polymerization of olefins with catalysts in liquid form. However, when a liquid catalyst is employed in gas phase polymerization, several phenomena can occur. First, the catalyst tends to deposit on the polymer forming the fluidized bed which in turn leads to accelerated polymerization on the surface of the particles of the bed. As the coated resin particles increase in size, they are exposed to a higher fraction of catalyst solution or spray because of their increased cross-sectional dimensions. If too much catalyst is deposited on the polymer particles, they can grow so large that they cannot be fluidized thereby causing the reactor to be shut down.
Second, using liquid catalyst under conditions of high catalyst activity, e.g., a liquid metallocene catalyst, the initial polymerization rate is often so high that the newly formed polymer particles can soften or melt, adhering to larger particles in the fluidized bed which can cause reactor shutdown. On the other hand, if the polymer particles size is too small, entrainment can occur resulting in fouling of the recycle line, compressor, and cooler and increased static electricity leading to sheeting can result.
However, there is no specific teaching as to the manufacture of a stereoregular polymer, such as isotactic polypropylene (iPP) and the conditions required to achieve same.
The present invention teaches the use of particular soluble metallocene catalysts to produce stereoregular polymers in gas phase polymerizations wherein the catalysts are fed into a particle lean zone in the reactor. The metallocenes catalysts are bridged bis-(substituted indenyl) compounds.